Unable to hot reload C# in .NET 9 Preview 6

[davidortinau]

Create a new Maui Project add the code below in app.cs
#if DEBUG
[assembly: System.Reflection.Metadata.MetadataUpdateHandlerAttribute(typeof(HangulClock.HotReloadService))]

public static class HotReloadService
{
#pragma warning disable CS8632 // The annotation for nullable reference types should only be used in code within a '#nullable' annotations context.
    public static event Action<Type[]?>? UpdateApplicationEvent;
#pragma warning restore CS8632 // The annotation for nullable reference types should only be used in code within a '#nullable' annotations context.

    internal static void ClearCache(Type[]? types) { }
    internal static void UpdateApplication(Type[]? types) {
        //if ((types != null && types.Length > 0 && types[0] != null))
        //{
            UpdateApplicationEvent?.Invoke(types);
        //}
    }
}

Then in content page add the code below: 

ContentPage:

C#
public MainPage()
{
#if DEBUG
       HotReloadService.UpdateApplicationEvent += (obj) =>
       {
           MainThread.BeginInvokeOnMainThread(() =>
           {
               Build();
           });
           
       };
#endif
}

#endif

Type: Bug

My code

void Build()
	{
		Content = new VerticalStackLayout
		{
			Spacing = 20,
			Margin = 20,
			Children = {
				(label = new Label {  
					Text = "Welcome to .NET MAUI!",
					FontSize = 64,
					TextColor = Colors.Blue
				}),
				(entry = new Entry { Placeholder = "Enter your name" }),
			}
		};

		label.SetBinding(Label.TextProperty, static (Entry e) => e.Text, source: entry);
	}

If I first hit CMD+S then the output I get is:

17:45:7 💡 Possible changes were found.
17:45:9 No changes were found.

And from then on in that debug session even hitting the hot reload fire button doesn't work.

When I instead hit fire button as the first action of the debug session, then CMD+S works as well as the button. I've confirmed that several times now.

Also, previously I encountered a situation with the button not appearing. Since the "solution" was updating VS Code Insider, I'm unable to repro right now. I have experience though several times when reloading the window and restarting extensions won't fix an issue, but upon applying a pending VS Code update the issue resolves.

Testing Android, the hot reload option (fire button) wasn't appearing in the debug button list. I reloaded the window, got some error about a connecting being closed, and reloaded again... Finally I saw that VS Code Insider wanted to apply an updated, so I figured what do I have to lose. After restarting I am now able to see the button for hot reload when debugging Android, except that I cannot debug the app and there is not .NET Hot Reload output window option. It's like the debugger is hung, probably on some invisible hot reload breakpoint. When I stop debugging I see the app (was frozen on the splash). Restarting debugging does fully initialize and I can interact with the app. After hitting the hot reload button I can now see the option for the output window.

Extension version: 1.9.2
VS Code version: Code - Insiders 1.92.0-insider (b23e791eb5afbd95f05aa24da7693ce89344a079, 2024-07-09T05:03:50.549Z)
OS version: Darwin arm64 23.5.0
Modes:

System Info

Item	Value
CPUs	Apple M1 Pro (8 x 2400)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled
Load (avg)	4, 5, 4
Memory (System)	16.00GB (0.05GB free)
Process Argv	--crash-reporter-id fc80353a-ef2a-479f-83ff-be5b061d3542
Screen Reader	no
VM	0%

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py29gd2263:31024238
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dsvsc013:30777762
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pythonregdiag2:30926734
pythonmypyd1:30859725
2e7ec940:31000449
pythontbext0:30879054
accentitlementst:30870582
dsvsc016:30879898
dsvsc017:30880771
dsvsc018:30880772
cppperfnew:30980852
pythonait:30973460
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9c06g630:31013171
a69g1124:31018687
dvdeprecation:31040973
dwnewjupytercf:31046870
nb_pkg_only:31057982
nativerepl1:31093711
refactort:31084545
pythonrstrctxt:31089940
4930e709:31088354
1iic9185:31091668

[spadapet]

@davidortinau, I couldn't repro, here's what I did:

• Installed .NET 9 preview 6 on MacOS
• dotnet new maui
• Opened that new maui folder in VSCode (has pre-release extensions for C#, C# Dev Kit, and .NET MAUI)
• Added all the code from your description
• Build and run on Mac Catalyst
• Made a minor code change and save file - C# hot reload detects changes and succeeds
• Made a minor code change and click fire button - also works
• The MetadataUpdateHandler was also triggered and built the new content

I think the description wasn't precise enough and I'm missing something. Can you attach the repro project? Or record a video?
Thanks!

[davidortinau]

Yes Preview 6 now works. I've also confirmed that. Preview 7 is when it doesn't work and I've detailed that issue here #1389